Ware fare is responsive to technological advances, and usually in a much delayed way. It took a long time for nations to realize just how much gunpowder changed warfare, for example, and even now we are having difficulty adapting 20th century tactics to 21st century warfare.
Aside from Aerial scouting, the Somme (July - Nov of 1916) was essentially the same tactics as had been in use for the prior 30 years. And so, it was a meatgrinder for both sides, albeit somewhat reduced for the Allies. The Tanks didn't actually have much effect...
The US Revolutionary War (1775-1790, or 1775-1817, depending upon whom one asks within the historical profession) was essentially fought with tactics unchanged since about 1500: line up, advance to firing range, and put as many volleys of lead in as one can.
As a generalization, however, every war is fought with the tactics developed from the misuse of the tech of the prior war. GySgt Bradley beat that into our skulls in HS...
The D&D magic isn't going to radically alter the general paradigm unless it's rather more common than has been portrayed in the town building rules (especially those for 3.X)... simply not enough of them except for acolytes. Healing from battle will be much faster, but the actual battles will largely remain infantry vs infantry, with officers on mounts, and a few archers in support. (Keep in mind - a 10% archer force can break a non-archer-supported force quickly... as was repeatedly shown in the lowlands of Scotland. Picts vs Romans, English vs Scots during the "braveheart" era, and the Reiver era... )
What the presence of a wizard will do is open the formations up to skirmishers rather than blocks. Something that, generally, is a mark of the 20th C. (With some exceptions - the French & Indian war, the US 1870's indian wars, the Border Reivers of Scotland, certain late shogunate samurai...)
When it comes down to it, I think you really need to remember that these mages you've got leading the army are going to be both skilled in the art of war and also quite possibly some of the most intelligent people in the world. Now, this of course leads to faults as really smart villains obsess over details and do not like anything to be out of their control.
Smart guys leading not so smart forces usually results in epic failure to communicate, and or haring off from the established plan because they fail to coordinate with the higher-ups. See also General Pickett, Col William Custer, Col Andrew Jackson, Admiral Bull Halsey... Hell, Jackson lead a battle well over a month AFTER the armistice was signed... and still managed to get elected president.
It's been said that the best soldiers are only just bright enough to accomplish the common tasks, and the best officers only a bit smarter than that. Bright soldiers tend to disobey. Dim ones trust there's a valid reason for the task. You want reasonably smart, but not too smart, officers. For the same reasons. Smart enough to implement their part of the plan, not so smart as to protect their men when it doesn't seem to be working yet.